1. Field of the Invention
The present invention relates to a method of mounting a drive circuit and the like on a substrate having a wide area, which is used in various kinds of flat displays, a liquid crystal sensor, a liquid crystal shutter or the like, and to a circuit substrate for use in the method and shaped in a stick.
2. Description of the Related Art
Flat panel display panels, such as a liquid crystal display, a plasma display, an electroluminescence (EL) display or a light emitting diode (LED) display, are popular as display devices. In each of these display panels, a transparent electrode, which constitutes many display dots (pixels) arranged in a matrix, is generally formed in a pattern on a transparent glass substrate with high precision, and a drive circuit and so on are connected to a pectinate electrode on the margin of the substrate.
Conventionally, in order to mount a drive circuit and the like on a display substrate of a display panel, for example, a method which connects an electrode of a printed board with a drive circuit mounted thereon and an electrode of a display substrate through a connector of a flexible circuit, or the like, is used. However, since the coloration and enlargement of a display has been recently advanced and the interelectrode pitch on a side of a panel has been narrowed, the Tape Automated Bonding (TAB) method, the Chip On Glass (COG) method or the like has come into use.
The TAB method bonds a drive element (chip), such as a semiconductor integrated circuit (IC), to a tape formed by laminating copper on a film carrier made of polyimide, polyester and so on and patterning an electrode thereon, and connects the tape and the drive chip to an electrode portion on the margin of a display substrate by soldering or thermocompression bonding. On the other hand, the COG method directly mounts a bare circuit element (bare chip) on the margin of a display substrate. In the case of the TAB method, since a resin film made of polyimide, polyester or the like is used for the tape, the interelectrode pitches of the tape and the display substrate differ due to the difference in coefficient of thermal expansion therebetween if the tape has a wide area. Therefore, it is difficult to connect the tape and the display substrate, and incorrect operations are likely to be caused after the connection. It is said that the limit of the pitch interval is approximately 100 .mu.m. The COG method does not have such a limit and can cope with the increase in the number of pins in an IC with the increase in the number of pixels
However, since such a conventional circuit mount method according to COG method directly mounts the chip on the display glass substrate, it is difficult to inspect, replace or repair a defective IC, and it is necessary to change a circuit pattern on the display glass substrate in accordance with the design of the IC. Therefore, a defect of a part of the wide glass substrate leads to a defect of the whole substrate, the yield is low, the cost is high, and it is difficult to merchandize a display panel.